【作者】 孙克淋；

【导师】 安伟光；

【作者基本信息】 哈尔滨工程大学 ， 固体力学， 2008， 博士

【摘要】 船体结构在建造和使用过程中很可能产生结构性缺陷(如初始变形、凹陷、开孔、裂纹等),由于设计和使用的需要,有些船板需要开孔,这些因素导致船体结构可靠性降低,而其中的某些缺陷可能产生危险的后果,导致事故发生。因此,从安全的角度考虑,如何精确地估算船体结构的实际承载能力以及产生缺陷后的极限剩余强度,并更科学、更合理地进行船舶结构设计和计算,已成为当今船舶力学界研究的一个热点课题。本文围绕这些问题开展的具体工作如下:1.结合板的非线性控制方程和有限元计算结果,讨论了具有初始缺陷(初始变形和焊接应力)、凹陷缺陷、开孔缺陷、裂纹缺陷板格的极限强度公式。给出了以完整结构极限强度和缺陷为参数的板格极限强度公式,从而便于建立具有缺陷结构的安全余量,为具有缺陷结构的可靠性分析提供理论基础。2.给出了结构可靠性敏度分析方法,分析了各种缺陷因素(初始缺陷、凹陷、开孔、裂纹)对板格极限强度可靠性指标的影响。分析表明:(1)对于具有初始缺陷的板格,无论板格柔度如何,都应严禁使用具有严重初始变形的板格,严格控制使用具有一般初始变形的板格,尽量减少使用具有轻微初始变形的板格。在板格柔度较小时,尽量减小焊接残余应力,在板格柔度相对较大时,应严格控制焊接残余应力;(2)对于具有凹陷的板格,要严格控制凹陷直径的大小,合理控制凹陷的深度;(3)对于具有开孔的板格,应尽量开圆孔,减小开孔尺寸,以保证板格具有足够的安全裕度;(4)对于具有初始裂纹的板格,无论载荷和裂纹的形式如何都应严格控制裂纹尺寸。3.结合具有缺陷板格的极限强度公式,给出了具有缺陷的板元减缩刚阵和反向节点力的显性表达式,为结构系统在失效过程中的力学分析提供参考,使残余结构的力学分析更加符合工程实际。4.建立随机船舶结构可靠性分析的一般模型,将结构力学计算的基本变量,如位移、弹性模量、单元的几何参数等直接放到安全余量中,使安全余量的数学模型更贴近原始状态(不是简单写成抗力和内力的关系,如Z=R(抗力)-S(内力)),给出了用基本变量显示的表达式,提高结构系统可靠性的计算精度。结合某型船舶的结构形式,考虑板格初始缺陷、凹陷、开孔、初始裂纹等因素,对某型船舶结构中的一个舱段进行具有缺陷结构的系统可靠性分析,并与完整结构系统可靠性进行比较。分析表明,由于缺陷的存在,舱段结构系统可靠度有明显的降低,特别是在假定的具有几何变形部位处板的可靠性指标降低的程度更大。因此,要严格控制初始缺陷的大小使其在一般缺陷范围内,对于重要结构一定要将缺陷控制在小缺陷范围内。更多还原

【Abstract】 Structural defectiveness occurs in the process of building and use of hull in all probability,such as initial distortion,concavity,hole,crackle and so on. Because of the requirements of design and use,some holes need to be drilled in the plate.The decrease of the reliability of hull structure is induced by those factors.And the danger may occur as a result of some defectiveness.Indeed,the accident may be also induced.Therefore,considering the safety,how to accurately estimate the actual carrying capacity of the hull and the ultimate remnant v after the defectiveness occurring,and also how to carry out the design and computation of the marine structure more scientifically and reasonably,all of these have been a pop topic in the field of ship mechanics.The work concerning these problems has been done in this paper,such as follows:1.Combining the nonlinear control equation of plate and the results of the FEM,the expressions of ultimate strength of the plate grid,which has initial defectiveness(initial distortion and welded stress),concavity,hole,or crackle,are discussed separately.Taking the ultimate strength of integral structure and the defectiveness as parameters,the formulae of ultimate strength of plate grid are given.Consequently,it is convenient for establishing the safety margins of defective structure,and all those provide the theoretical basis for reliability analysis of defective structure.2.The sensitivity analysis method of the structural reliability is given.The influence of every kind of defectiveness(initial distortion,concavity,hole,and crackle) on the reliability index is analyzed.The analysis indicates that,(1) for the plate grid with initial defectiveness,whatever the flexibility is,the use of that with severe initial distortion should be declined,and the use of that with general initial distortion should be controlled strictly,and also the use of that with slight initial distortion should be limited furthest.When the flexibility of plate grid is less,the welded remnant stress should minish furthest,and when the flexibility is larger, the welded remnant stress should be controlled strictly;(2) for the plate grid with concavity,the diameter of concavity should be controlled strictly,and the depth of that should be controlled reasonably;(3) for the plate grid with hole,the dimension of the hole should be controlled strictly and be less than a certain range, in order to ensure the plate grid with enough reliability reserves.If the circinal hole can be made,do it.Or if not,the dimension of the hole should be minish furthest;(4) for the plate grid with initial crackle,whatever the load and the form of crackle are,the dimension of crackle should be controlled strictly.3.Combining the formula of ultimate strength of plate grid with defectiveness,the reducing stiffness matrix and the obvious expression of reverse node force of the plate unit with defectiveness are given,which provides reference to mechanics analysis of the structural system in the progress of failure,and makes the mechanics analysis of the remanent structure more coincident with engineering practice.4.The general model of stochastic reliability analysis of marine structure is established.The basic variables in the calculation of structural mechanics,such as displacement,elastic modulus,geometrical parameter of the unit and so on,are taken into the safety margin directly.The mathematic model of safety margin is made more close to its original state(not be simply described as the relationship between resistance and internal force,such as Z=R-S,where,R is resistance and S is internal force).The obvious expression of safety margin with basic variables is given,and the calculational precision of the structural system reliability is increased.Combining the structural form of the certain ship and considering the factors of initial defectiveness,concavity,hole,and initial crackle etc,the system reliability analysis of one cabin block of the certain marine structure is carried out,and the cabin block is compared with the structure system which has no defectiveness.The analysis indicates that,because of the defectiveness,the reliability index of structure system of the cabin block reduces obviously,and especially,that of the plate with supposed geometrical distortion reduces more.Thus,the size of initial defectiveness should be controlled strictly and be made in the general range.For the important structure,the size of defectiveness must be controlled in the small range.更多还原